What Disguise said about himself pretty much applies to anyone. There is no known way to turn .j2ts into other images, seeing as you do not claim to have JJ2, JCS, or anything else. That said, if you see a tileset you like, say, through a screenshot, you must contact the author and ask for the source file.
Of course, you should not use any tileset (err... in a seperate game) without the author's permission. A few of them might actually care, you know.